synopsisAcrylonitrile grafts readily to granular corn starch in aqueous slurry when initiated by hydrogen peroxide plus activator. Prime evidence for grafting lies in the ease of separating PAN from starch in high yield when the initiator is arobisisobutyronitde rather than peroxide. Grafting efficiencies are determined by extraction with appropriate solvents: dimethylformamide for homo-PAN, and Looiling water for ungrafted starch. Grafting efficiencies of PAN range from 78 to 95%, M,, values for grafted PAN are 4,000 to 90,O00, and frequency of attachment of side chains range from 300 to 1100 glucose units per chain. Increasing the monomer level, a t fixed initiator concentration, tends to result in longer rather than more frequent side chains. AN behaves much as has been previously found for MMA, but the somewhat more efficient grafting at more frequent intervals and the more nearly uniform distribution of polymer in the starch granule suggest that AN penetrates the starch granule more readily than MMA. INTRODUCTIONThe grafting of poly(methy1 methacrylate) (PMMA) to granular corn or its unsaturated esters3 by way of free-radical initiation has been described in previous papers from this laboratory. Means of separating ungrafted homopolymer of methyl methacrylate from the graft haye been studied in detaiL4 This paper reports results of similar techniques used to prepare and characterize grafts of PAN (polyacrylonitrile) to granular corn starch.Grafting of PAN to starch has already b&n carried out, but under conditions widely dzerent from those here reported. Walrath et a1.6 prepared grafts to wheat starch by mutual or preirradiation from a ' W o source. Kimura and co-workers grafted by initiation with ceric salt in solutions of potato amylose6 or by use of reprecipitated starch peroxidized with ozone.' Fanta et a1.8 studied the effects of reaction conditions on composition of product obtained by initiation with ceric nitrate in dilute solutions of wheat starch. EXPERIMENTAL MaterialsUnmodified and hypochlorite-oxidized starches were A. E. Staley production materials. The unmodified starch was defatted prior to use as free of nonvolatiles and readily polymerjzable, was used as received. All other reactants were reagent grade or equivalent. PolymerizationThe procedure was the same as previously described for methyl methacrylate.' On addition of the peroxide to the mixture containing all other reactants, the temperature rose from its initial 30°C. to a peak within the next 15 min. Total reaction time was 60-90 min. The product was filtered, washed with water, and dried in air a t room temperature. Conversion of monomer to polymer was 95% or higher in each instance, except for those runs initiated with AIBN (azobisisobutyronitrile). Characterization of RESULTS AND DISCUSSION Qualitative Description of ProductsThe products are recovered in the form of fine white powders, similar in appearance to the original starch. Even the appearance of individual particles is changed hardly a t all by the polymerization, as shown...
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